Automatic Reference Counting, or ARC, was added to the Objective-C language in 2011 with iOS 5 and Mac OS X 10.7. Prior to ARC, you had to manage the memory usage of your app manually with calls to methods such as -retain, -release, and -autorelease. ARC manages these calls automatically at compile time, and, as such, does not allow you to call them yourself.

As @Paulw11 mentions in his comment, you should be able to replace that line with